1. Field
One or more embodiments relate to a fuel cell stack and a fuel cell system including the fuel cell stack.
2. Description of the Related Art
A fuel cell generates electric energy from materials abundant on the earth. An example is hydrogen. The fuel cell is being focused on as one of a number of environmentally friendly alternative energy technologies, which also includes solar cells. Generally, a fuel cell has a stack structure having a stack of cells. Each cell generates unitary power. For the generation of a large amount of power, either the number of cells constituting a fuel cell stack is increased, or a plurality of fuel cell stacks are connected either in parallel or in series.
Generation efficiency of a fuel cell stack is determined by a ratio of a quantity of power generated by the fuel cell stack to a quantity of fuel supplied to the fuel cell stack. Generally, fuel, the quantity of which is at or above a predetermined amount, is supplied to a fuel stack to maintain a constant quantity of fuel injected into the fuel stack even in a case of a partial load at which a ratio of the quantity of power consumed by a load to the quantity of generatable power is less than or equal to 50%. The reason for this is that inlet gas pressure equal to or above a predetermined value is necessary for fuel to flow within a fuel cell stack. Thus, when a fuel cell stack operates at partial load, generation efficiency of the fuel cell stack is deteriorated.